When sourcing a used machine, you must prioritize the Nominal Pressure (Tonnage) and the Table Length. Ensure the tonnage is sufficient for your thickest materials; for example, bending 6mm mild steel typically requires significantly more pressure than 1mm aluminum. Check the Stroke Distance and Maximum Open Height to ensure they accommodate your specific tooling and workpiece dimensions. Additionally, verify the Backgauge Precision (e.g., ±0.05mm) and the CNC System brand (such as Delem, Cybelec, or ESA), as these directly impact the machine's accuracy and ease of programming.